Donald Trump Denied Teresa Giudice's Request for Letter Supporting Husband Joe

Teresa Giudice turned to Donald Trump right before Joe got locked up in 2016, hoping he would write a letter vouching for her husband ... TMZ has learned.

Sources close to the Giudices tell TMZ ... Teresa reached out to Trump several months before Joe started serving his 41-month sentence, and asked Donald to write a character letter. This was before he was elected President, but she hoped the letter would help Joe get a lighter sentence.

Our sources say she and Trump got along while she was on the fifth season of the 'Celebrity Apprentice' in 2012, so we're told she thought she'd give it a shot. Nothing ventured, nothing gained ... but it didn't work.

We're told Trump's office -- and not Trump himself -- wrote a letter back saying he would NOT be able to do anything for her with regards to Joe. His staff wished her and her family well, FWIW.

As you know, Trump went on to become Prez ... and Joe went on to enter a federal prison. Joe was just ordered to be deported back to Italy once he's out of prison.

Joe's crime was a federal offense, so it's at least possible Trump could pardon him. Take 2, Teresa?